.TH std::experimental::pmr::polymorphic_allocator::construct 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::experimental::pmr::polymorphic_allocator::construct \- std::experimental::pmr::polymorphic_allocator::construct

.SH Synopsis
   template< class U, class... Args >                     \fB(1)\fP (library fundamentals TS)
   void construct( U* p, Args&&... args );
   template< class T1, class T2, class... Args1, class...
   Args2 >

   void construct( std::pair<T1, T2>* p,                  \fB(2)\fP (library fundamentals TS)
                   std::piecewise_construct_t,
                   std::tuple<Args1...> x,

                   std::tuple<Args2...> y );
   template< class T1, class T2 >                         \fB(3)\fP (library fundamentals TS)
   void construct( std::pair<T1, T2>* p );
   template< class T1, class T2, class U, class V >       \fB(4)\fP (library fundamentals TS)
   void construct( std::pair<T1, T2>* p, U&& x, V&& y );
   template< class T1, class T2, class U, class V >
   void construct( std::pair<T1, T2>* p, const            \fB(5)\fP (library fundamentals TS)
   std::pair<U, V>& xy );
   template< class T1, class T2, class U, class V >
   void construct( std::pair<T1, T2>* p, std::pair<U,     \fB(6)\fP (library fundamentals TS)
   V>&& xy );

   Constructs an object in allocated, but not initialized storage pointed to by p the
   provided constructor arguments. If the object is of type that itself uses
   allocators, or if it is std::pair, passes this->resource() down to the constructed
   object.

   1) If std::uses_allocator<U, memory_resource*>::value == false (the type U does not
   use allocators) and std::is_constructible<U, Args...>::value == true, then
   constructs the object as if by ::new((void *) p) U(std::forward<Args>(args)...);.

   Otherwise, if std::uses_allocator<U, memory_resource*>::value == true (the type U
   uses allocators, e.g. it is a container) and std::is_constructible<U,
   std::allocator_arg_t, memory_resource*, Args...>::value == true, then constructs the
   object as if by ::new((void *) p) U(std::allocator_arg, this->resource(),
   std::forward<Args>(args)...);.

   Otherwise, if std::uses_allocator<U, memory_resource*>::value == true (the type U
   uses allocators, e.g. it is a container) and std::is_constructible<U, Args...,
   memory_resource*>::value == true, then constructs the object as if by ::new((void *)
   p) U(std::forward<Args>(args)..., this->resource());.

   Otherwise, the program is ill-formed.

   2) First, if either T1 or T2 is allocator-aware, modifies the tuples x and y to
   include this->resource(), resulting in the two new tuples xprime and yprime,
   according to the following three rules:

   2a) if T1 is not allocator-aware (std::uses_allocator<T1, memory_resource*>::value
   == false) and std::is_constructible<T1, Args1...>::value == true, then xprime is x,
   unmodified.

   2b) if T1 is allocator-aware (std::uses_allocator<T1, memory_resource*>::value ==
   true), and its constructor takes an allocator tag (std::is_constructible<T1,
   std::allocator_arg_t, memory_resource*, Args1...>::value == true, then xprime is
   std::tuple_cat(std::make_tuple(std::allocator_arg, this->resource()), std::move(x)).

   2c) if T1 is allocator-aware (std::uses_allocator<T1, memory_resource*>::value ==
   true), and its constructor takes the allocator as the last argument
   (std::is_constructible<T1, Args1..., memory_resource*>::value == true), then xprime
   is std::tuple_cat(std::move(x), std::make_tuple(this->resource())).

   2d) Otherwise, the program is ill-formed.

   Same rules apply to T2 and the replacement of y with yprime.

   Once xprime and yprime are constructed, constructs the pair p in allocated storage
   as if by ::new((void *) p) pair<T1, T2>(std::piecewise_construct, std::move(xprime),
   std::move(yprime));.

   3) Equivalent to construct(p, std::piecewise_construct, std::tuple<>(),
   std::tuple<>()), that is, passes the memory resource on to the pair's member types
   if they accept them.

   4) Equivalent to

   construct(p, std::piecewise_construct, std::forward_as_tuple(std::forward<U>(x)),
                                          std::forward_as_tuple(std::forward<V>(y)))

   5) Equivalent to

   construct(p, std::piecewise_construct, std::forward_as_tuple(xy.first),
                                          std::forward_as_tuple(xy.second))

   6) Equivalent to

   construct(p, std::piecewise_construct,
   std::forward_as_tuple(std::forward<U>(xy.first)),

    std::forward_as_tuple(std::forward<V>(xy.second)))

.SH Parameters

   p       - pointer to allocated, but not initialized storage
   args... - the constructor arguments to pass to the constructor of T
   x       - the constructor arguments to pass to the constructor of T1
   y       - the constructor arguments to pass to the constructor of T2
   xy      - the pair whose two members are the constructor arguments for T1 and T2

.SH Return value

   \fI(none)\fP

.SH Notes

   This function is called (through std::allocator_traits) by any allocator-aware
   object, such as std::vector, that was given a std::polymorphic_allocator as the
   allocator to use. Since memory_resource* implicitly converts to
   polymorphic_allocator, the memory resource pointer will propagate to any
   allocator-aware subobjects using polymorphic allocators.

.SH See also

   construct     constructs an object in the allocated storage
   \fB[static]\fP      \fI(function template)\fP
   construct     constructs an object in allocated storage
   \fI(until C++20)\fP \fI(public member function of std::allocator<T>)\fP

.SH Category:
     * Noindexed pages
